Improvement in yields for semiconductor devices is a continuous goal. One area that may be improved is process uniformity across the workpiece in the radial direction. In certain processes, the workpiece may receive more treatment near the center of the workpiece.
For example, a deposition process may deposit more material near the center of a workpiece than near the outer edge of that workpiece. This may be due to the increased plasma density near the center of the deposition chamber.
As another example, a heated implant may provide a different dose near the outer edge, since this outer edge of the workpiece may be somewhat cooler than the rest of the workpiece.
In another example, a spin coating process may leave more material near the outer edge of the workpiece, as compared to the center of the workpiece. This may be due to the centripetal force pushing the coating toward the outer edge of the workpiece.
In each of these examples, this process non-uniformity in the radial direction may negatively impact the yield of a semiconductor workpiece. In some cases, efforts are made to improve the uniformity of the process. However, there may be limits to the degree of uniformity that may be achieved.
Therefore, it would be beneficial if there were a method of selectively processing the outer portion of a workpiece. Further, it would be advantageous if this selective processing improved the overall process uniformity of the workpiece.